Juvenile rheumatoid arthritis (JRA) is the most common chronic inflammatory disease in children, and may be related to genetics. Having two siblings who both have JRA in one family is rare. The purpose of this registry is to collect patient information and blood samples from qualifying JRA siblings and their families. The goal of the registry is to further understanding of JRA as related to genetics. JRA is the most common chronic inflammatory pediatric rheumatic disease. JRA may be related to a complex genetic trait. It is rare to have two or more affected siblings, or sibpairs, within one family. The JRA ASP (Affected Sibpair) Registry is a nationwide effort and will collect information and blood samples from JRA sibpairs and their families. Unaffected family members (e.g., mother, father, and unaffected children) are also invited to participate. Patients and their families may enroll in the registry in one of two ways: patients may contact the registry directly, or they may be referred to the registry through their physician. Once the family has qualified to join the registry, the family will be asked to complete a questionnaire on the medical history of their JRA-affected members. Physicians of the JRA-affected members will be asked to complete questionnaires about their patients'conditions. Family members will also be invited to provide a one-time blood sample. Information collected through the registry will help researchers identify genes involved in JRA susceptibility.